The present invention relates to an optical information record medium and improvement of corrosion resistance of a recording layer formed on a substrate made of polycarbonate resin.
The optical record system has such characteristics or advantages as handiness that enables non-contact recording/reproduction, high durability in dirt or scratches, and a storage capacity several tens or hundred times larger than a conventional magnetic record system utilizing electromagnetic induction, for example, that it is not only utilized as a so-called compact disk or a laser disk wherein audio signals or video signals are digitally recorded, but also is anticipated to be used in filing code information or image information with great storage capacity.
Among the optical information record media, there is a wide variety of write once type optical disks, or magneto optical disks, other than the aforementioned compact disks that are only for reproduction, but each of them consists of an information record layer formed on a transparent substrate made of a polycarbonate resin.
A polycarbonate resin is a suitable material for a substrate of the optical information record medium since it has such features as: having thermal resistance at the time of melt molding and can be molded with ease; being not transformed or changed in quality after disk molding; and having supreme mechanical characteristics.
On the other hand, as for a record material of the informaiion record layer, metallic record materials such as rare earth elements-transition metal amorphous alloy membranes used in an magneto optical disk have been exploited. For example, materials such as TbFeCo, TbFe, GdFe have been reported to be desirable in sensitivity or reading capability, etc.
In order to utilize an optical information record medium having an information record layer made of aforementioned metallic record material, there is a as to how to improve its corrosion resistance.
In fact, when an optical information record medium such as a compact disk or an magneto-optical disk having a substrate made of a polycarbonate resin form is stored under high temperature and high humidity, a corrosion originates in a record film or a reflection film. An inferior reproduction is caused due to the corrosion, so it is a serious problem for an optical information record medium that affects its reliability.